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Risks and causes of molar pregnancy

Men and women discussing gestational trophoblastic tumours

This page has information about the risk factors and causes of molar pregnancy. There is information about

 

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Risks and causes of molar pregnancy

A risk factor is anything that can increase your chance of developing a disease or condition. We don’t yet know what causes molar pregnancy, but we do know of some factors that increase the risk.

Molar pregnancies are very rare. A complete molar pregnancy is when there is no foetal tissue in the womb at all. There is only molar tissue. This type of molar pregnancy is much more common in teenage mothers and mothers over the age of 40. In a partial molar pregnancy some foetal tissue is formed. Age doesn't affect the risk of developing a partial molar pregnancy.

Molar pregnancies are more common in women from Asian countries than in those from other ethnic groups. In Asian women in the UK, the incidence is about 1 molar pregnancy for every 380 babies born, compared to around 1 for every 590 pregnancies in the UK.

If you have already had one molar pregnancy, you have about a 1 or 2 in 100 chance (1 to 2%) of having another one. If you have had two or more molar pregnancies your risk of having another is about 15 to 20 out of 100 (15 to 20%).

Some studies seem to show an increase in the risk of molar pregnancy in women who eat low levels of carotene (found in orange or yellow fruits and vegetables) and fat. 

Hormone levels may play a part. Women who have used the birth control pill may have a slightly higher risk of molar pregnancy than other women.

 

CR PDF Icon You can view and print the quick guides for all the pages in the about molar pregnancy section.

 

 

What a molar pregnancy is

A molar pregnancy occurs when the fertilisation of the egg by the sperm goes wrong and leads to the growth of abnormal cells or clusters of water filled sacs inside the womb. This condition is a type of gestational trophoblastic tumour. The link takes you to general information about these tumours.

 

What a risk factor is

A risk factor is anything that can increase your chance of developing a disease or condition. Each condition has different risk factors. Researchers have not yet been able to identify what causes molar pregnancies, but we do know of some factors that increase a woman's risk of developing this type of tumour.

Remember that having a risk factor does not mean that you will definitely get a particular medical condition. Most women who have one or more risk factors never develop a molar pregnancy, and some people who have none of the risk factors do develop one. This is only a guide to what may increase risk. Gestational trophoblastic tumours are rare. In the UK, there is about 1 molar pregnancy for every 590 pregnancies.

 

Age

Molar pregnancy is an abnormal pregnancy, so all women who become pregnant have a slight risk of developing it. However, researchers have found that some types of molar pregnancy are more common in certain age groups. Complete molar pregnancies are more common in teenage mothers and mothers over the age of 45. But age does not affect the risk of partial molar pregnancies.

 

Ethnicity

Molar pregnancies are more common in women from Asian countries than in those from other ethnic groups. However, recent studies show that in Asia, and in Asian women living in the UK, the incidence is now about 1 molar pregnancy for every 380 babies born, compared to around 1 for every 590 babies born in the UK overall.

 

Previous molar pregnancy

If you have already had one molar pregnancy, you have about a 1 or 2 in 100 chance (1 to 2%) of having another one. This means that more than 98 out of every 100 women (98%) who become pregnant after a molar pregnancy will have a normal pregnancy. If you have had two or more molar pregnancies your risk of having another is higher, at about 15 to 20 out of 100 (15 to 20%).

 

Diet

Some studies in the past showed an increase in the risk of molar pregnancy in women who ate low levels of carotene (found in orange or yellow fruits and vegetables) and fat. So these dietary factors may affect the risk of molar pregnancy but we don't have other evidence to confirm this.

 

Taking the birth control pill

Taking the oral contraceptive pill for a long time may increase your risk of developing a molar pregnancy, although results of studies have varied. But if you have had a molar pregnancy, your doctor will advise you not to take the pill until your urine and blood hCG tests go back to normal. This is because some studies have shown that using the contraceptive pill before the molar pregnancy has completely gone may mean that you are more likely to have persistent trophoblastic disease and to need chemotherapy.

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Updated: 31 August 2012